1. Field of the Invention
The present invention relates to cooling systems for gas turbines and more particularly to a cooling system for cooling a turbine wheel of a gas turbine and the attachment portions of turbine blades.
2. Description of the Related Art
Main components of a gas turbine include a compressor for compressing air, a combustor for combusting the compressed air with fuel, and a turbine for converting the thermal energy of the resultant combustion gas into rotational energy. Air is suctioned into the compressor where it is compressed, and the compressed air is sent to the combustor where it is combusted with fuel, turning into a high-temperature combustion gas. The combustion gas is then fed to the turbine where it expands. The turbine drives the compressor, and the rest of the output of the turbine is used to drive a load such as a power generator or the like.
The temperature of such combustion gas exceeds 1,000 degrees Celsius; thus, the turbine blades and vanes located at the combustion gas passage and the nearby surfaces of the casing and rotor also have high temperatures. Since the temperatures of the turbine blades and the rotor become high when exposed to high-temperature gas, the turbine wheels to which the turbine blades are attached via their attachment portions also become high in temperature, necessitating cooling of these components. However, the turbine rotor that includes the turbine wheels is a rotary component, which means that difficulties are involved in supplying cooling air to the turbine rotor from its outer circumferential side.
JP-2005-320875-A discloses a method for cooling a turbine wheel of a gas turbine and the attachment portions of turbine blades. In the method, an adjusting unit for adjusting the flow rate or pressure of compressed air is detachably disposed at the entrance of a cooling air passage that directs the compressed air bled from a compressor toward a turbine rotor via the central hole provided in an intermediate shaft that connects a compressor rotor and the turbine rotor. Thus, compressed air with the appropriate flow rate and pressure is directed into the wheel space of the turbine and into the turbine rotor and can be used as sealing air as well as cooling air.